1. Field of the Invention
The present invention relates to a main switch conveying apparatus for a vacuum circuit breaker, and more particularly to a conveying apparatus capable of conveying a main switch of a vacuum circuit breaker in such a manner that the main switch can be coupled/separated to/from an electric load or source terminals installed at a rear position of a cage of the vacuum circuit breaker and can be stopped at a safety position, a test position, and a run position of the vacuum circuit breaker.
2. Description of the Prior Art
As generally known in the art, vacuum circuit breakers are used for protecting circuits and appliances by rapidly breaking circuits simultaneously with quick extinguishing arc, which is generated during an opening/closing operation of such vacuum circuit breakers under a normal load state or when shutting off fault current, in a vacuum container.
Hereinafter, a conventional main switch conveying apparatus for a vacuum circuit breaker will be described with reference to FIGS. 1 to 6. The conventional main switch conveying apparatus for a vacuum circuit breaker shown in FIGS. 1 to 6 had been proposed as the German patent DE10006427C2, which was filed and patented by the same applicant as the one of this invention. FIG. 1 is a perspective view showing a structure of a conventional vacuum circuit breaker, FIGS. 2 and 3 are perspective views showing a conventional main switch conveying apparatus for the vacuum circuit breaker, FIG. 4 is a partially sectional view showing a structure of the conventional main switch conveying apparatus for the vacuum circuit breaker, FIG. 5 is a partially enlarged view showing a conventional nut assembly positioned in a safety position, and FIG. 6 is a partially enlarged view showing the conventional nut assembly positioned in a run position.
Referring to FIG. 1, the main switch conveying apparatus for the conventional vacuum circuit breaker includes a carriage 100 for conveying a main switch 140 loaded on the carriage 100 in such a manner that the main switch 140 is coupled/separated to/from electrical load and source terminals 130 installed at a rear portion of a cage 120, a carriage actuator assembly 200 for actuating the carriage 100 to move in a forward direction or a rearward direction, and a girder assembly 300 for supporting the carriage actuator assembly 200.
The carriage 100 includes a box shaped body 101 formed at an outer peripheral portion thereof with a wall section 101a (referred to FIG. 2) and an upper portion of which is opened, and two pairs of wheels 102 installed at both sides of the body 101 in such a manner that the wheels 102 can move in forward and rearward directions along guide rails (not shown) installed at both inner sidewalls of the cage 120.
As shown in FIGS. 2 to 4, the carriage actuator assembly 200 includes a lead screw 201 extending by passing through a perforated hole 201b formed in a front portion of the wall section 101a of the box body 101, a conveying nut 202 installed at an inner front portion of the wall section 101a of the body 101 in such a manner that the conveying nut 202 is screw-coupled with the lead screw 201, a U-shaped bracket 203 fixed to the body 101 in order to prevent the conveying nut 202 from being decoupled from the lead screw 201, and a handle 213 detachably coupled to a front end of the lead screw 201 in order to allow a user to rotate the lead screw 201 in a forward direction or a reverse direction.
The conveying nut 202 is formed with a female screw section, which is meshed with the lead screw 201. Two guide recesses 202b having inclined surfaces are formed at upper and lower surfaces of outer circumferential of the conveying nut 202 respectively and a guide slot 202c is formed on the outer circumferential of the conveying nut 202 between the two guide recesses 202b. 
In addition, a rudder 209 fixed to a rear end of the lead screw 201 can stably move in a forward direction or in a rearward direction along a pair of travel rails 212 and 212′ installed at an inner portion of the body 101 of the carriage 100 in a length direction of the body 101.
The girder assembly 300 includes a support structure 303 having a cavity therein and supporting a bearing such that rotational force is transferred to the front end of the lead screw 201, which passes through a fixing hole formed at a center of the support structure 303, left and right sliding plates 304a installed in inner portions of both sides of the support structure 303 such that the left and right sliding plates 304a slidably move in left and right directions, left and right handles 305 and 305′ fixed to the left and right sliding plates 304 and outwardly protruded from the support structure 303, and a spring (not shown) for biasing the left and right sliding plates 304a such that ends of the left and right sliding plates 304a are inserted into insertion holes 120a formed at both sidewalls of the cage 120.
In addition, a pair of limit pin assemblies 204 are provided in the vicinity of the conveying nut 202 so as to restrict a rotation of the conveying nut 202 in such a manner that the carriage 100 together with the conveying nut 202 is stopped at a pull out position (test position) or a connection position of the terminals and the main switch (run position) respectively.
As shown in FIGS. 5 and 6, the limit pin assemblies 204 are mounted on a U-shaped bracket 203 and a pair of support plates 211 vertically installed on the U-shaped bracket 203 to surround the nut 202. The pin assemblies 204 include limit pins 205 and 205′ aligned symmetrically in a diagonal direction of the bracket 203 and one of the limit pins 205 and 205′ detachably is inserted into one of the two guide recesses 202b of the nut 202 exclusively to stop the nut 202 together with the carriage 100. The limit pins 205 and 205′ are connected to left and right drive pins 207 and 207′ via links 206 and 206′. In addition, the left and right drive pins 207 and 207′ are elastically biased to drive the limit pins 205 and 205′ into a position of releasing the nut 202 rotatably by a pair of springs 208 and 208′. A guide pin 210 is inserted into a guide slot 202c of the conveying nut 202 for guiding the conveying nut 202 to mesh with the lead screw 201 stably.
Reference numerals 141, 142, 214 and 500 represent bus bars, an interrupter, a bearing and the conveying apparatus.
In order to assemble the conventional vacuum circuit breaker having the main switch conveying apparatus 500, the conveying apparatus 500 is firstly mounted on the cage 120. Then, after moving the sliding plates 304a towards a center of the girder assembly 300 by manipulating left and right handles 305 and 305′ of the girder assembly 300, the girder assembly 300 is positioned in the cage 120. After that, the ends of the sliding plates 304a are inserted into insertion holes 120a formed in the sidewalls of the cage 120, thereby fixing the girder assembly 400 to the cage 120.
In this state, the carriage 100 is moved in the forward direction so as to couple the main switch 140 to the terminals 130. In operation, electric current from an electric source is applied to the vacuum interrupter (not shown) installed at an inner portion of the main switch 140 through an upper bus bar 141. Such current is outputted through a lower bus bar (not shown) to a electric load via terminals 130. When an accident current such as a large current due to a circuit shortage or over current etc. occurs during the operation, the interrupter instantaneously shuts off the circuit by separating a movable contact from a stationary contact in the container of the interrupter.
Then, the operation that the main switch 140 is separated from the terminals 130 for maintenance work such as test is explained as follows. Firstly, in an initial state in which the main switch 140 is coupled to the terminals 130, a worker couples the handle 213 to the front end of the lead screw 201. Then, if the worker rotates the lead screw 201 counterclockwise, the conveying nut 202 and carriage 100 moves to approach the girder assembly 300 along the lead screw 201. Thus, the main switch 140 is moved backwards so that the main switch 140 is separated from the terminals 130.
After performing repair work in a state in which the main switch 140 has been separated from the terminals 130, the operation that the main terminals 140 is again coupled to the terminals 130 is explained as follows. At this time, the worker rotates the lead screw 201 clockwise by manipulating the handle 213, so the carriage 100 moves to depart from the girder assembly 300 so that the main switch 140 is coupled to the terminals 130.
The movement of the conveying nut 202 on the lead screw 201 in the forward or rearward direction is restricted by the limit pin assembly 204. When the carriage 100 has been completely pulled out to approach the girder assembly 300 as shown in the FIG. 3, in other words at the test position, the conveying nut 202 has been completely moved in the rearward direction along the lead screw 201 so that the right drive pin 207′ contacts with one side wall of the girder assembly 300. Thus, the limit pin 205′ is apart from the guide recess 202b, so that the conveying nut 202 idles without moving in the forward or rearward direction.
However, the above mentioned main switch conveying apparatus is only adaptable for moving the main switch between two positions, such as the test position and the run position of the vacuum circuit breaker. In a recent power distribution system, it is required that the main switch should be positioned between three positions, such as a safety position, a test position and a run position, for improving safety. Thus, the conventional main switch conveying apparatus is not adaptable for a state-of-art vacuum circuit breaker. Although it is possible to move the main switch between three positions by modifying the structure of the conventional main switch conveying apparatus, the number of parts is increased, an assembling process thereof is complicated, and a manufacturing cost thereof is increased while lowering a preciseness of an operation.
In addition, since a braking apparatus for stopping and locking the carriage at each of the three positions is not provided, a worker cannot easily recognize the position of the main switch of the vacuum circuit breaker. Thus, the worker manipulates the main switch conveying apparatus in the reverse direction of his intention, the carriage can be moved to the reverse direction of user's intention, so that risk is high.